This invention relates to an improved hydrometallurgical method of treating zinc plant residue, to obtain zinc sulphate solution which is substantially free of iron.
Leaching of calcined zinc ores or concentrates is a well known method of providing zinc sulphate solution, from which zinc may then be recovered by electrolysis. However, a substantial part of the zinc in the material being leached remains, primarily as zinc ferrite, in an undissolved residue which must be further treated to provide economic recovery of the zinc initially present.
Various methods have been suggested for the recovery of the zinc values from these residues, for example roasting the residue with a concentrated sulphuric acid to solubilize the zinc value. Also, leaching the residue at a variety of temperatures and pressures with sulphuric acid, under both oxidizing and reducing conditions, has been suggested. However, none of these methods have been found completely acceptable, primarily because they do not provide economic recovery of zinc and sulphur values from materials used to give reducing conditions or to neutralize excess acid.